Watermelon [Citrullus lanatus], is an important commercial member of the Cucurbitaceae family. The fruits display a wide range of coloring on the outside rind. Color in the edible tissue varies from different shades of red to orange to yellow to white. Additional variation in the marketplace can be found with both seeded and seedless types. Unlike the flesh coloring—which is caused by varying genetic loci—the distinction between seeded and seedless varieties is usually caused by varying the ploidy levels.
It is known that there is a correlation between ploidy level and flesh firmness. (U.S. patent application Ser. No. 12/856,286, which is incorporated herein in its entirety). Diploid lines typically have the lowest flesh firmness levels. For reasons that are unclear, the process of changing a diploid line to a tetraploid line correlates with firmer fruit flesh, and thus, tetraploid lines usually have firmer fruit flesh than diploids. Triploids, being a cross between a tetraploid and a diploid, have an intermediate level of fruit firmness.
There is increasing consumer demand in the fresh produce business for products that combine quality and convenience. Examples of products that meet these criteria included bagged mini-carrots and leafy crops, like lettuce and spinach. Similarly, there is a demand for mature cut fruits, like watermelon, melon, mango, pineapple, papaya, and kiwi. In watermelon fruits, one consumer quality criteria is sweetness. Sweetness can be estimated by measuring the total soluble solids, or Brix, using a refractometer. Indeed, fruit quality standards for Brix levels have been established (United States Standards for Grades of Watermelon, U.S. Department of Agriculture (1978)). According to these standards, edible parts of the fruit having not less than 8 Brix are deemed to be “Good,” while edible parts of the fruit having not less than 10 Brix are deemed to be “Very Good.”
A growing segment of watermelon retail sales are offering to the consumer fruits that are cut and displayed with the rinds attached, or fruits with the rinds removed and where the edible flesh is cut into smaller pieces. The industry term for these products is “minimally processed.” In 1998, Perkins-Veazie et al. [(1998) Hortscience 33:605] estimated that 10% of the retail watermelon market was minimally processed.
In addition to offering convenience to the consumer, one advantage of cut fruit displays is that the consumer can visually inspect the quality of the fruit, and in particular, judge whether the fruit is mature and ready to consume. Often, immature fruits will not be uniform in pigmentation, and overripe fruit will display signs of decay.
The disadvantage to the produce retailer in presenting minimally processed watermelon products is that cut fruits have a short shelf life. Studies suggest that minimally processed products have a short shelf life of about 2 to 3 days maximum (ibidem; Wehner et al. In: Watermelons: Characteristics, Production and Marketing. Maynard, editor. ASHS Press, Alexandria Va. 2001).
Watermelon fruits currently available typically undergo rapid quality deterioration after being cut. Deterioration is manifested as juice leakage; in some varieties, the flesh of a fresh cut watermelon fruit becomes unattractive to the consumer quickly. Cutting the fruit also causes decay, which is observed as a softening of the fruit texture. The rapid deterioration of cut watermelon fruit places both time and space constraints on the retailer. Because cut fruits have a short shelf life, the retailer typically performs the processing on the retail site, and has to monitor the products often to ensure that deteriorating products are discarded.
Unlike the sweetness standards established by the U.S. Department of Agriculture, there are no industry standards to describe the firmness of the edible portions of watermelon fruits. Thus, there are a wide range of descriptors in use, such as “firm” and “crisp” (Erma Zaden catalog descriptors for varieties Gil 104 and Erma 12), “very firm flesh” by Zhang et al. (US Patent Pub. Nos. 2004/0060085 and 2003/0217394) and by Seminis Vegetable Seeds, Inc. in their Watermelon catalog to describe the variety Cooperstown. Seminis also has described cultivars Fenway, Royal Star, and Sentinel as having “excellent crispness,” “firm flesh,” and “crisp juicy flesh,” respectively. Rogers Seed Company advertises the Tri-X Brand 626 as “exceptionally firm” and the Tri-X Brand 313 as having “a firm texture” and “crispness of flesh.”
While advertising terminology used to describe watermelon fruit flesh firmness is quite variable, quantitative measurements show that commercial germplasm prior to this invention have low fruit firmness. Therefore, there is a need in the marketplace for watermelon lines that produce fruits that have a longer shelf life when processed.